LAUSR

ABSTRACT Growth responses of trees and shrubs to climate often exhibit unexplained variation in alpine regions, making it difficult to predict how they will respond to future changes in climate. We sought to characterize and explain this variability in southwest Yukon, a topographically complex region of subarctic Canada. We collected cores and sections from 360 spruce trees and 480 willow shrubs across treelines on north and south aspects in six valleys spanning two mountain ranges. We compared growth rates, growth patterns, and climate-growth responses between species and topographic factors. South aspects had wider tree rings and higher tree and shrub interseries correlations than north aspects, likely because of shallow active layers on the latter. Growth patterns and responses to climate did not vary between aspects or elevations but differed slightly between mountain ranges, likely because of differences in spring soil moisture content between ranges. Growth responses of both species to summer temperature were positive, but tree growth was negatively correlated to spring temperature and shrub growth was negatively correlated to summer precipitation, both of which are projected to increase along with summer temperature. Future changes in climate could therefore reduce the growth of one or both species in southwest Yukon.